The Internet consists of a network of interconnected computer networks. Each of these computers has an IP address that is comprised of a series of four numbers separated by periods or dots and each of these four numbers is an 8-bit integer which collectively represent the unique address of the computer within the Internet. The Internet is a packet switching network whereby a data file routed over the Internet to some destination is broken down into a number of packets that are separately transmitted to the destination. Each packet contains, inter alia, some portion of the data file and the IP address of the destination.
The IP address of a destination is useful in routing packets to the correct destination but is not very people friendly. A group of four 8-bit numbers by themselves do not reveal or suggest anything about the destination and most people would find it difficult to remember the IP addresses of a destination. As a result of this shortcoming in just using IP addresses, domain names were created. Domain names consist of two or more parts, frequently words, separated by periods. Since the words, numbers, or other symbols forming a domain name often indicate or at least suggest the identity of a destination, domain names have become the standard way of entering an address and are more easily remembered than the IP addresses. After a domain name has been entered, a domain name server (DNS) resolves the domain name into a specific IP address. Thus, for example, when someone surfing the Internet enters into a browser program a particular domain name for a web site, the browser first queries the DNS to arrive at the proper IP address.
IP addresses are typically assigned to the computer networks of the Internet or autonomous systems (“ASs”). An autonomous system is a collection of IP addresses and IP-capable devices and communications links under a single administrative domain. An autonomous system assigned the IP addresses can include one or more organizations, universities or companies, such as Internet Service Providers (“ISPs”). A particular AS may be assigned a range of IP addresses and each host within an AS can be assigned an IP address. For example, a single AS may have the IP addresses 128.66.64.0 through 128.66.64.255, with each IP address corresponding to a host. In order to ensure that information is routed to the correct destination, each AS must be able to determine how to reach the AS that is assigned the destination address. Therefore, each AS can announce its range to other ASs on the Internet. Other ASs can use this information to ensure that the data packet reaches the AS assigned the destination address and, therefore, the destination.
The use of reverse DNS has been problematic for several reasons (determining a domain name from an IP address), including reverse DNS is not required for the Internet to work properly (unlike forward DNS) and there are no restrictions on reverse DNS naming. Because reverse DNS is not required for the Internet to work properly, owners of IP address blocks or groups do not always provide reverse DNS entries for their IP addresses except in cases where it helps in the maintenance of the owners' networks. The routers on the Internet backbone are generally configured with good, consistent reverse DNS entries. However, moving away from the Internet backbone, many organizations, such as ISPs, do not configure reverse DNS entries for the hosts away from the Internet backbone.
Additionally, an ISP can provide any domain name for a reverse DNS entry, because there are no restrictions on reverse DNS naming. An ISP can, for example, use an domain name for a host corresponding to an IP address in its address space even if the ISP does not own the domain name or even if the domain name is not allocated. An ISP can also use a top level domain for a host corresponding to an IP address in its address space even though the top level domain does not exist.